Transparent Bridge Network After STA Is

The spanning-tree calculation occurs when the bridge is powered up and whenever a topology change is detected. The calculation requires communication between the spanning-tree bridges, which is accomplished through configuration messages (sometimes called bridge protocol data units, or BPDUs). Configuration messages contain information identifying the bridge that is presumed to be the root (root identifier) and the distance from the sending bridge to the root bridge (root path cost)....

Apple Talk Enhanced IGRP Clients Cannot Connect to Servers

Symptom Macintosh clients cannot connect to servers in an AppleTalk Enhanced IGRP network environment. Table 9-11 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers For information on troubleshooting this problem, see the section AppleTalk Enhanced IGRP Routers Not Establishing Neighbors later in this chapter. For...

Apple Talk Technology Basics

AppleTalk was designed as a client server distributed network system. In other words, users share network resources (such as files and printers) with other users. Computers supplying these network resources are called servers computers using a server's network resources are called clients. Interaction with servers is essentially transparent to the user because the computer itself determines the location of the requested material and accesses it without further information from the user. In...

ATM Label Switching

ATM uses label switching, a technique in which a simple label is placed in the header of each cell. The label provides information used in transporting the cell across the next hop in the network. Networks that do not use label switching usually require each packet (or cell) to contain the explicit address of the final destination. ATM uses label switching because it is simpler, thereby making faster switching possible. 1 A switching unit reads an incoming cell from a particular port. The...

Basic Port Checks

The following steps outline the procedure for performing basic port checks. It is important to perform basic port checks to verify that a LightStream 2020 port is enabled and functioning correctly Step 1 Use the show port port-number all command to display information about a port. Step 2 Check the Admin Status field to make sure that the port is up. Step 3 Check for excessive line errors, packet drops, or a lack of receive data. If there is no receive data or if the error rate on the receive...

Booting Client ARP Requests Timeout During Netboot

Verify that neighbor routers can ping the server. Use the trace exec command to determine the path to the server. Use the show arp privileged exec command to examine the ARP1 tables or the show ip route privileged exec command to view the IP routing table. Verify that the server is listed and that the routing table entries are appropriate. Use the clear arp-cache and clear ip-route privileged exec commands to force the router to repopulate its ARP and routing tables. Shut down all extra...

Booting Router Hangs After ROM Monitor Initializes

Symptom When a user is booting a Cisco 7000 series, AGS+, AGS, ASM-CS, MGS, IGS, or CGS router from ROM, the system hangs after the ROM monitor initializes. Table 3-19 outlines the problems that might cause this symptom and describes solutions to those problems. Table 3-19 Booting Router Hangs After ROM Monitor Initializes Table 3-19 Booting Router Hangs After ROM Monitor Initializes Inspect EPROM size jumpers. Refer to the hardware installation and maintenance publication for your router to...

Booting the Router

Cisco routers can initialize the system (boot) in four ways Netboot Routers can boot from a server using the Trivial File Transfer Protocol (TFTP), the DEC Maintenance Operation Protocol (MOP), or the Remote Copy Protocol (RCP) across any of the supported media types (such as Ethernet, Token Ring, Fiber Distributed Data Interface FDDI , High-Speed Serial Interface HSSI , and serial lines). Flash memory Routers can boot from Flash memory, a nonvolatile storage medium that can be electrically...

Booting Timeouts and Outof Order Packets Prevent Netbooting

Symptom Timeouts or out-of-order packets prevent successful netbooting. The number oftimeouts and out-of-order packets indicated on the router's console display might vary. The following example shows a netbooting session that contains excessive timeouts and out-of-order packets Booting gs3-bfx from 131.108.1.123 O.O .O O OOO.O .O.O The client router might boot in this situation. However, when excessive timeouts and out-of-order packets occur, there is probably a network problem, and netbooting...

Catalyst 1600 Token Ring Switch Startup

When you start up a Catalyst 1600 Token Ring switch, the self-test program automatically checks to see whether the switch is operating correctly. The self-test begins by testing low-level hardware functions and then conducts high-level self-tests. During the high-level self-test, the LCD panel displays the following The version number of the boot software, and the date and time that the software was released The number of each stage in the self-test (these are usually displayed too quickly for...

Catalyst 2900 Series Startup

When you start up a Catalyst 2900 series LAN switch, the following should occur The PS LED on the supervisor engine module faceplate should come on and stay green while power is applied to the system. The system fan assembly and Fan LED should come on and stay on while power is applied to the system. The Status LED on the supervisor engine module and on each interface should be orange until the boot is complete. When the system boot is complete, the supervisor engine module initializes the...

Catalyst 5000 Series Startup

When you start up a Catalyst 5000 series LAN switch, the following should occur The PS1 and PS2 LEDs on the supervisor engine module faceplate should be green. The system fan assembly should be operating and the Fan LED on the supervisor engine module should come on. The Status LED on the supervisor engine module and all interfaces should be orange until the boot is complete. When the system boot is complete, the supervisor engine module should initialize the switching modules. The status LED...

Cell Relay Packet Handling

Cell relay is a flexible and responsive method for multiplexing all forms of digital traffic (data, voice, image, and video). Cell relay can handle rapid changes in the quantity and pattern of the traffic in the network. All traffic is placed in fixed-length packets of information (cells) and switched at high speeds. Cell relay is generally acknowledged as the best multiplexing technology for modern communication applications because it combines the strengths of TDM and conventional packet...

Cip Claw Connection Does Not Come Up

Symptom Common Link Access for Workstations (CLAW) connections do not come up properly over a Channel Interface Processor (CIP). The output of the show extended channel slot port statistics exec command shows N for CLAW connections, indicating that they are down. Table 10-13 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-13 CIP CLAW Connection Does Not Come Up Table 10-13 CIP CLAW Connection Does Not Come Up Step 1 Check whether TCP IP is...

Cisco 7000 Series Startup

When you start up a Cisco 7000 series router, the following should occur The DC OK LED should go on and should remain on as long as the system is receiving source power. The fans should be operating. The Route Processor (RP) Normal LED should go on and stay on to indicate normal system operation the Halt CPU LED should remain off. The Enabled LED on the Switch Processor (SP) or Silicon Switch Processor (SSP) and each interface processor should go on when the RP has completed initialization of...

Cisco 7500 Series Startup

When you start up a Cisco 7500 series router, the following should occur The AC (or DC) OK LED should go on immediately and should remain on as long as the system is receiving power. The blower should be operating. The Route Switch Processor (RSP) and front-panel Normal LEDs should go on (to indicate normal system operation) and should remain on during system operation the CPU Halt LED should remain off. The Enabled LED on each interface processor should go on (to indicate that the RSP has...

Cisco View Timeout Error Messages

Symptom When attempting to use the CiscoView application, you receive timeout messages and cannot view a device. Table 23-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-7 CiscoView Timeout Error Messages Table 23-7 CiscoView Timeout Error Messages Perform the steps outlined in the section Testing Basic Connectivity and Setup earlier in this chapter. Try increasing the polling interval. To increase the polling interval, select Options,...

Cisco Works Sync with Sybase Fails

Symptom Attempts to run Sync with Sybase in CiscoWorks fail. Table 23-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-2 CiscoWorks Sync with Sybase Fails Table 23-2 CiscoWorks Sync with Sybase Fails Follow the steps outlined in the section Testing Basic Connectivity and Setup earlier in this chapter. Run nmadd from the command line to determine whether the problem is related to community string, name resolution, or timing out. The nmadd...

Configuration Management Deviceto Database or Databaseto Device Does Not

Symptom The device-to-database or the database-to-device operation in the Configuration Management application does not work. Table 23-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-5 Configuration Management Device-to-Database or Database-to-Device Does Not Run Table 23-5 Configuration Management Device-to-Database or Database-to-Device Does Not Run Perform the steps outlined in the section Testing Basic Connectivity and Setup Perform...

Configuration Register DIP Switch

Cisco 7000 series running Software Release 9.17(4) or later (Flash netboot) or Cisco IOS Release 10.0 or later (ROM) Cisco 7000 series running Software Release 9.17(4) or later (Flash netboot) or Cisco IOS Release 10.0 or later (ROM) Cisco 7000 running Software Release 9.21 or earlier from ROM Cisco IGS running Software Release 9.1 or later Cisco IGS running software prior to Software Release 9.1

Configuration SnapIn Manager Cannot Modify DoItNow

Symptom The DoItNow operation in the Configuration Snap-In Manager application does not work. Table 23-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-6 Configuration Snap-In Manager Cannot Modify DoItNow Table 23-6 Configuration Snap-In Manager Cannot Modify DoItNow Perform the steps outlined in the section Setup earlier in this chapter. Testing Basic Connectivity and Perform the steps outlined in the section earlier in this chapter....

Data Command Frames

Data command frames vary in size, depending on the size ofthe information field. Data frames carry information for upper-layer protocols command frames contain control information and have no data for upper-layer protocols. In data command frames, a frame control byte follows the access control byte. The frame control byte indicates whether the frame contains data or control information. In control frames, this byte specifies the type of control information. Following the frame control byte are...

Datagram Delivery Protocol

AppleTalk's primary network-layer protocol is the Datagram Delivery Protocol (DDP). DDP provides connectionless service between network sockets. Sockets can be assigned either statically or dynamically. AppleTalk addresses, which are administered by the DDP, consist of two components a 16-bit network number and an 8-bit node number. The two components are usually written as decimal numbers, separated by a period (for example, 10.1 means network 10, node 1). When an 8-bit socket identifying a...

DECnet Connections to DEC Hosts Fail over Router End Node Problem

Symptom DECnet nodes cannot communicate when attempting to make connections over routers. Note This section focuses on problems in end nodes. For router-related problems and solutions, see the section DECnet Connections to DEC Hosts Fail over Router (Router Problem) later in this chapter. Table 11-1 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-1 DECnet Connections to DEC Hosts Fail over Router (End Node Problem) Step 1 Check the end...

DECnet Connections to DEC Hosts Fail over Router Router Problem

Symptom DECnet nodes cannot communicate when attempting to make connections over routers. Note This section focuses on problems in the router. For end node-related problems and solutions, see the section DECnet Connections to DEC Hosts Fail over Router (End Node Problem) earlier in this chapter. Table 11-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-2 DECnet Connections to DEC Hosts Fail over Router (Router Problem) Use the show decnet...

DECnet End Nodes Cannot Find Designated Router

Symptom End nodes cannot find a designated router. End nodes cannot access nodes that are on different LANs, but other nodes connected to the same LAN are accessible. Table 11-3 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-3 DECnet End Nodes Cannot Find Designated Router DECnet not enabled on Step 1 Use the show running-config privileged exec command to view the router router configuration. Determine whether DECnet global configuration...

DECnet No Phase IV Connectivity over Phase V Backbone

Symptom Communication between DECnet Phase IV areas separated by an ISO CLNS (Phase V) backbone fails. Phase IV nodes cannot communicate with other Phase IV nodes across a Phase V cloud. However, nodes can communicate with one another within the same Phase IV cloud. Note For more information about troubleshooting DECnet OSI internetworks, see Chapter 12, Troubleshooting ISO CLNS. Table 11-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-7...

DECnet Router or End Node Sees Incorrect Designated Router

Symptom Routers and end nodes see an incorrect or an unexpected designated router. If your network requires a specific router to be elected the designated router, allowing another router to become a designated router can cause unpredictable network behavior and can block connectivity in and out of the area. Table 11-4 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-4 DECnet Router or End Node Sees Incorrect Designated Router Priority of...

DECnet Routers Not Establishing Adjacencies

Symptom Routers do not establish adjacencies with other routers on the same LAN. Table 11-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-5 DECnet Router Not Establishing Adjacencies Router area number is higher than configured decnet max-area DECnet limits the number of adjacencies that can be established by a router to 32. Step 1 Enable the debug decnet events privileged exec command to determine whether the adjacency is being...

Descriptions of Environment Variables

The following are descriptions of the CiscoWorks environment variables NMSROOT Default directory for CiscoWorks installation. If the software was installed in a different directory, substitute the appropriate directory path to ensure the correct definition of the NMSROOT environment variable. SYBASE Default directory for Sybase installation. If the software was installed in a different directory, substitute the appropriate directory path to ensure the correct definition of the SYBASE...

Dialin Modem Cannot Send or Receive IP Data

Symptom After a dialin connection is established, a modem cannot send or receive IP data. Note For general problems associated with a modem that cannot send or receive data, refer to the section Dialin Modem Cannot Send or Receive Data earlier in this chapter. Note For information on troubleshooting IP problems not specific to dialin connections, refer to Chapter 7, Troubleshooting TCP IP. Table 16-10 outlines the problems that might cause this symptom and describes solutions to those problems....

Dialin Modem Hangs Up Shortly After Connecting

Symptom A dialin connection is successful but the modem hangs up after 30 to 90 seconds. Table 16-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 16-5 Dialin Modem Hangs Up Shortly After Connecting Possible Causes Suggested Actions Table 16-5 Dialin Modem Hangs Up Shortly After Connecting Use the show line exec command on the access server or router. The output for the auxiliary port should indicate the currently configured Tx1 and Rx2 For...

Dialin No Connectivity Between Modem and Router

Symptom The connection between a modem and a Cisco access server or router does not work. Attempts to initiate a reverse Telnet session to the modem have no result, or the user receives a connection refused by foreign host message. Note More specific symptoms for dialin connection problems are covered later in this chapter. Table 16-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 16-2 Dialin No Connectivity Between Modem and Router Possible...

Distance Vector Multicast Routing Protocol

Distance Vector Multicast Routing Protocol (DVMRP), defined in RFC 1075, uses a technique called reverse path flooding. With reverse path flooding, on receipt of a packet, the router floods the packet out all paths except the path that leads back to the source of the packet, which ensures that a data stream reaches all LANs. If the router is attached to a LAN that does not want to receive a particular multicast group, the router sends a prune message back to the source to stop the data stream....

Establishing a Reverse Telnet Session to a Modem

If you are running Cisco IOS Release 11.0 or earlier, you must establish a reverse Telnet session to configure a modem to communicate with a Cisco device. As long as you lock the data terminal equipment (DTE)-side speed of the modem (see Table 16-5 for information on locking the modem speed), the modem will always communicate with the access server or router at the desired speed. Be certain that the speed of the Cisco device is configured prior to issuing commands to the modem via a reverse...

Ethernet and IEEE 8023

Ethernet and IEEE 802.3 specify similar technologies. Both are CSMA CD LANs. Stations on a CSMA CD LAN can access the network at any time. Before sending data, CSMA CD stations listen to the network to see if it is already in use. If it is, the station wishing to transmit waits. If the network is not in use, the station transmits. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously. In this case, both transmissions are damaged, and the...

Fault Management Mechanisms

Token Ring networks employ several mechanisms for detecting and compensating for network faults. For example, one station in the Token Ring network is selected to be the active monitor. This station, which can potentially be any station on the network, acts as a centralized source of timing information for other ring stations and performs a variety of ring maintenance functions. One of these functions is the removal of continuously circulating frames from the ring. When a sending device fails,...

Fault Tolerant Features

FDDI provides a number of fault-tolerant features, the most important of which is the dual ring. If a station on the dual ring fails or is powered down or if the cable is damaged, the dual ring is automatically wrapped (doubled back onto itself) into a single ring, as shown in Figure 5-4. In this figure, when Station 3 fails, the dual ring is automatically wrapped in Stations 2 and 4, forming a single ring. Although Station 3 is no longer on the ring, network operation continues for the...

FDDI Specifications

FDDI is defined by four separate specifications (see Figure 5-1) Media Access Control (MAC) Defines how the medium is accessed, including frame format, token handling, addressing, an algorithm for calculating a cyclic redundancy check value, and error recovery mechanisms. Physical Layer Protocol (PHY) Defines data encoding decoding procedures, clocking requirements, framing, and other functions. Physical Layer Medium (PMD) Defines the characteristics of the transmission medium, including the...

Figure 111 DNA and the OSI Reference Model

As Figure 11-1 shows, DNA supports a variety of media and link implementations. Among these are well-known standards such as Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), IEEE 802.2, and X.25. DNA also offers a traditional point-to-point link-layer protocol called Digital Data Communications Message Protocol (DDCMP) and a 70-Mbps bus used in the VAX cluster called the computer-room interconnect bus (CI bus).

Figure 114 Examples of DECnet Addresses

DECnet hosts do not use manufacturer-assigned Media Access Control (MAC)-layer addresses. Instead, network-level addresses are embedded in the MAC-layer address according to an algorithm that multiplies the area number by 1,024 and adds the node number to the product. The resulting 16-bit decimal address is converted to a hexadecimal number and appended to the address AA00.0400 in byte-swapped order, with the least significant byte first. For example, DECnet address 12.75 becomes 12363 (base...

Figure 152 show controllers cbus Command Output

Switch Processor 5, hardware version 11.1, microcode version 10.7 512 Kbytes of main memory, 128 Kbytes cache memory 4 256 byte buffers, 4 1024 byte buffers, 312 1520 byte buffers 1024 byte system buffer Restarts 0 line down, 0 hung output, 0 controller error FSIP 0, hardware version 1.0, microcode version 175.0 Microcode loaded from system Interface and attached cable information Interface 0 - Serial 0 0, electrical interface is Universal (cable unattached) 22 buffer RX queue threshold, 23...

Figure 155 Extended ping Specification Menu

Datagram size 100 64 specification Extended commands n yes - Extended commands Source address selected option Data pattern OxABCD Oxffff - Data pattern Loose, Strict, Record, Timestamp, Verbose none specification Sweep range of sizes n Type escape sequence to abort. Sending 20, 64-byte ICMP Echos to 12 9.44.12.7, timeout is 2 seconds Packet has data pattern 0xFFFF Success rate is 100 percent, round-trip min avg max 1 3 4 ms In general, perform serial line ping tests as follows Step 1 Put the...

Figure 156 All Zeros 1500Byte ping Test

Target IP address 192.169.51.22 Repeat count 5 100 Datagram size 100 1500 Timeout in seconds 2 Extended commands n y Source address 192.169.51.14 Type of service 0 Set DF bit in IP header no Validate reply data no I Data pattern OxABCD 0x0000 Loose, Strict, Record, Timestamp, Verbose none Sweep range of sizes n Type escape sequence to abort. Sending 100, 1500-byte ICMP Echos to 192.169.51.22, timeout is 2 seconds Packet has data pattern 0x0000 Success rate is 100 percent (100 100), round-trip...

Figure 157 All Ones 1500Byte ping Test

Target IP address 192.169.51.22 Repeat count 5 100 Datagram size 100 1500 Timeout in seconds 2 Extended commands n y Source address 192.169.51.14 Type of service 0 Set DF bit in IP header no Validate reply data no Loose, Strict, Record, Timestamp, Verbose none Sweep range of sizes n Type escape sequence to abort. Sending 100, 1500-byte ICMP Echos to 192.169.51.22, timeout is 2 seconds Packet has data pattern 0xFFFF Success rate is 100 percent (100 100), round-trip min avg max 4 6 8 ms zounds

Figure 158 show buffers Command Output

Cookie-Monster> show buffers Buffer elements 401 in free list (500 max allowed) 87777499 hits, 0 misses, 0 created Small buffers, 104 bytes (total 120, permanent 120) 114 in free list (20 min, 250 max allowed) 70005538 hits, 6 misses, 2 trims, 2 created Middle buffers, 600 bytes (total 90, permanent 90) 88 in free list (10 min, 200 max allowed) 25696696 hits, 27 misses, 27 trims, 27 created Big buffers, 1524 bytes (total 90, permanent 90) total identifies the total number of buffers in the...

Figure 162 show line Command Output

Line 1, Location , Type Length 24 lines, Width 80 columns rate (TX RX) is 38400 38400, no parity, 2 stopbits, 8 databits abilities I Hardware Flowcontrol In, Hardware Flowcontrol Out Modem-Callout, Modem RI is CD Modem state I Line 1, Location , Type Length 24 lines, Width 80 columns rate (TX RX) is 38400 38400, no parity, 2 stopbits, 8 databits abilities I Hardware Flowcontrol In, Hardware Flowcontrol Out Modem-Callout, Modem RI is CD Modem state I Lial Chars Escape Hold Stop Start x none - -...

Figure 172 ISDN Physical Layer Frame Formats

A Activation bit B1 B1 channel bits B2 B2 channel bits D D channel (4 bits x 4000 frames sec 16 kbps) E Echo of previous D bit F Framing bit L Load balancing S Spare bit The frames are 48 bits long, of which 36 bits represent data. The bits of an ISDN physical layer frame are used as follows F Provides synchronization. L Adjusts the average bit value. E Used for contention resolution when several terminals on a passive bus contend for a channel. B1, B2, and D For user data. Multiple ISDN user...

Figure 181 The Frame Relay Frame

Field length, 12 Variable 2 1 Field length, 12 Variable 2 1 The 10-bit DLCI value is the heart of the Frame Relay header. It identifies the logical connection that is multiplexed into the physical channel. In the basic (not extended by the LMI) mode of addressing, DLCIs have local significance that is, the end devices at two different ends of a connection may use a different DLCI to refer to that same connection. Figure 18-2 provides an example of the use of DLCIs in nonextended Frame Relay...

Figure 192 X25 and the OSI Reference Model

End-to-end communication between DTEs is accomplished through a bidirectional association called a virtual circuit. Virtual circuits permit communication between distinct network elements through any number of intermediate nodes without the dedication of portions of the physical medium that characterizes physical circuits. Virtual circuits can be either permanent or switched (temporary). Permanent virtual circuits (PVCs) are typically used for the most often used data transfers, whereas...

Figure 194 The X121 Address Format

The addressing fields that make up the X.121 address are necessary only when an SVC is used, and then only during call setup. After the call is established, the PSN uses the LCI field of the data packet header to specify the particular virtual circuit to the remote DTE. Layer 3 X.25 uses three virtual circuit operational procedures call setup, data transfer, and call clearing. Execution of these procedures depends on the virtual circuit type being used. For a PVC, Layer 3 X.25 is always in data...

Figure 196 Output from the X25 Version of the show interfaces serial Command

SerialO is up, line protocol is up Hardware is MCI Serial Internet address is 131.63.125.14 255.255.255.0- MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec ely 255 255, load 1 255 Encapsulation X25, loopback not set __ I LAPB DTE, state CONNECT, modulo 8, k 7, N1 12056, N2 20 IFRAMEs 1 1 IRNRs 0 0 ReJs 0 0 SABM Es 1 0 FRMRs 0 Q DISCs 0 0 Not ready flow control count ress 170093, state R1 modulo 8, timer 0 Defaults cisco encapsulation, idle 0, nvc 1 input output window sizes 2 2, packet sizes 128...

Figure 202 Inaccurate Forwarding and Learning in Transparent Bridging Environments

Suppose Host A sends a frame to Host B. Both bridges receive the frame and correctly conclude that Host A is on Network 2. Unfortunately, after Host B receives two copies of Host A's frame, both bridges again receive the frame on their Network 1 interfaces because all hosts receive all messages on broadcast LANs. In some cases, the bridges will then change their internal tables to indicate that Host A is on Network 1. If this is the case, when Host B replies to Host A's frame, both bridges...

Figure 203 A Transparent Bridge Network Before STA Is

The first activity in spanning-tree computation is the selection of the root bridge, which is the bridge with the lowest-value bridge identifier. In Figure 20-3, the root bridge is Bridge 1. Next, the root port on all other bridges is determined. A bridge's root port is the port through which the root bridge can be reached with the least aggregate path cost. The value of the least aggregate path cost to the root is called the root path cost. Finally, designated bridges and their designated...

Figure 211 User Assignments on Communications Channel Using TDM

Time Time Time Time Time Time Time Time Time Time Time Time slot slot slot slot slot slot slot slot slot slot slot slot The time slots allocated for each user occur at precisely the same time in every frame. Because the time slots are synchronous, TDM is sometimes referred to as synchronous transfer mode (STM). Users can access the communications channel only when a time slot that has been allocated to them is available. For example, User A can send messages over the communications channel only...

Figure 2110 ATM Adaptation Layer Functions

When ATM cells are transferred through a network, each cell is processed in isolation from all other cells. All processing decisions are made based on the cell header no processing of the data in the payload field occurs. Figure 21-11 shows some examples of AAL processing. Figure 21-11 AAL Processing Examples Figure 21-11 AAL Processing Examples Hosts A and C are connected to the network through ATM interfaces, so they do all their AAL processing internally. The network does not do any...

Figure 2112 Information Flow Through AAL

Convergence sublayer (CS) user data is broken up into packets (CS-PDUs) Segmentation and reassembly (SAR) sublayer each CS-PDU is broken up into SAR-PDUs CS-PDU SAR-PDU SAR-PDU To ATM layer CS-PDU SAR-PDU SAR-PDU To ATM layer The convergence sublayer (CS) accepts higher-layer traffic for transmission across the network. Depending on the AAL type, header and or trailer fields are added to the packet. The packet is then segmented by the SAR sublayer to form 48-byte payloads (also known...

Figure 217 VCCs Transported Within VPs

Physical link in public or private network The ATM cell is the fixed-length transmission unit defined by the ATM standard. An ATM cell contains two major types of information the payload and the header. The payload is the information to be transferred through an ATM network. It can include data, voice, image, or video. The header is the information used to route the cell through the network and to ensure that the cell is forwarded to its destination. Every ATM cell is 53 bytes long. The first 5...

Figure 219 The User Network Interface ATM Cell Header Format

Table 21-2 Fields in an ATM Cell Header Table 21-2 Fields in an ATM Cell Header Controls the flow of traffic across the user network interface and thus into the ATM network. Second 4 bits of Byte 1 and the first 4 bits of Byte 2 Identifies a particular VPC3. A VPC is a group of virtual connections carried between two points and may involve several ATM links. VPIs provide a way to bundle traffic heading to the same destination. Second 4 bits of Byte 2, Byte 3, and the first 4 bits of Byte 4...

Figure 95 A Sample Apple Talk ZIT

AURP allows a network administrator to connect two or more AppleTalk internetworks through a foreign network (such as Transmission Control Protocol Internet Protocol TCP IP ) to form an AppleTalk wide-area network (WAN). The connection is called a tunnel, which functions as a single, virtual data link between the AppleTalk internetworks, as shown in Figure 9-6.

Fitting ATM into the OSI Model

ATM standards define protocols that operate at Layer 2 (the data link layer) of the International Organization for Standardization (ISO) seven-layer Open Systems Interconnection (OSI) reference model. Figure 21-3 shows the layered architecture of the OSI model. The data link layer is concerned with data transmission between two network switches. This layer is not concerned with the transmission of an entire message between a source and a destination switch this responsibility belongs to Layer 3...

Frame Format

FDDI frame formats (shown in Figure 5-7) are similar to those of Token Ring. The fields of an FDDI frame are as follows Preamble Prepares each station for the upcoming frame. Start delimiter Indicates the beginning of the frame. It consists of signaling patterns that differentiate it from the rest of the frame. Frame control Indicates the size of the address fields, whether the frame contains asynchronous or synchronous data, and other control information. Destination address Contains a unicast...

Frame Relay Technology Basics

Frame Relay provides a packet-switching data communications capability that is used across the interface between user devices (for example, routers, bridges, host machines) and network equipment (for example, switching nodes). User devices are often referred to as data terminal equipment (DTE), whereas network equipment that interfaces to DTE is often referred to as data circuit-terminating equipment (DCE). The network providing the Frame Relay interface can be either a carrier-provided public...

Implementing Hold Queue Limits

Hold queues are buffers used by each router interface to store outgoing or incoming packets. Use the hold-queue interface configuration command to increase the number of data packets queued before the router will drop packets. Increase these queues by small increments (for instance, 25 ) until you no longer see drops in the show interfaces output. The default output hold queue limit is 100 packets. Note The hold-queue command is used for process-switched packets and periodic updates generated...

Input Error Type Field Name

CRC errors occur when the CRC calculation does not pass (indicating that data is corrupted) for one of the following reasons Serial cable is too long or cable from the CSU DSU to the router is not shielded SCTE mode is not enabled on DSU CSU line clock is incorrectly configured Ones density problem on T1 link (incorrect framing or coding specification) Step 1 Ensure that the line is clean enough for transmission requirements. Shield the cable if necessary. Step 2 Make sure the cable is within...

Internet Group Membership Protocol

Internet Group Membership Protocol (IGMP), defined in RFC 1112, relies on Class D IP addresses for the creation of multicast groups. By using a specific Class D address, an individual host dynamically registers itself in a multicast group. Hosts identify their group memberships by sending IGMP messages. Traffic is then sent to all members of that multicast group. Routers listen to IGMP messages and periodically send out queries to discover which groups are active on which LANs. To build...

Internet Routing

Routing devices in the Internet have traditionally been called gateways an unfortunate term because elsewhere in the industry, the term gateway applies to a device with somewhat different functionality. Gateways (which we will call routers from this point on) within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control (such an entity is called an autonomous system)....

IP Enhanced IGRP Router Stuck in Active Mode

Symptom An IP Enhanced IGRP router is stuck in Active mode. Multiple Stuck-in-Active messages are sent to the console DUAL-3-SIA Route 198.169.52.51 Stuck-in-Active For a more detailed explanation of Enhanced IGRP Active mode, see the section Enhanced IGRP and Active Passive Modes later in this chapter. Note Occasional messages of this type are not a cause for concern. This is how an Enhanced IGRP router recovers if it does not receive replies to its queries from all its neighbors. However, if...

IPX Enhanced IGRP Router Stuck in Active Mode

Symptom An IPX Enhanced IGRP router is stuck in Active mode. The router repeatedly sends error messages similar to the following DUAL-3-SIA Route 3c.0800.0c00.4321 Stuck-in-Active Note Occasional messages of this type are not a cause for concern. This is how an Enhanced IGRP router recovers if it does not receive replies to its queries from all its neighbors. However, if these error messages occur frequently, you should investigate the problem. For a more detailed explanation of Enhanced IGRP...

IPX Enhanced Igrp Sap Updates Not Propagated by Router

Symptom Novell SAP packets are not forwarded through a router running IPX Enhanced IGRP. Clients might be unable to connect to servers over one or more routers, or they might connect only intermittently. Note Procedures for troubleshooting IPX Enhanced IGRP problems not specific to SAPs are described in the section IPX Enhanced IGRP No Connectivity over IPX Enhanced IGRP Router earlier in this chapter. Table 8-10 outlines the problems that might cause this symptom and describes solutions to...

Ipx Rip Sap Updates Not Propagated by Router

Symptom Novell SAP packets are not forwarded through a router running IPX RIP. Clients might be unable to connect to servers over one or more routers, or they might intermittently be able to connect. Note Procedures for troubleshooting IPX RIP problems not specific to SAPs are described in the section IPX RIP No Connectivity over IPX RIP Router earlier in this chapter. Additional problems relating to intermittent connectivity problems are described in the section Novell IPX Intermittent...

ISDN Components

ISDN components include terminals, terminal adapters (TAs), network-termination devices, line-termination equipment, and exchange-termination equipment. ISDN terminals come in two types. Specialized ISDN terminals are referred to as terminal equipment type 1 (TE1). Non-ISDN terminals such as DTE that predate the ISDN standards are referred to as terminal equipment type 2 (TE2). TE1s connect to the ISDN network through a four-wire, twisted-pair digital link. TE2s connect to the ISDN network...

Iso Clns Connections Fail Using Certain Protocols

Symptom Host connections fail using certain protocols. Hosts might be able to connect to other hosts using some protocols but are unable to connect using others. Table 12-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 12-6 ISO CLNS Connections Fail Using Certain Protocols Host is not configured to support the service Verify that the needed protocols are correctly installed and configured on the host system. Consult your vendor's...

Iso Clns Host Cannot Access Hosts in Different Area

Symptom Host cannot access hosts in a different area. Hosts in the same area are accessible. Table 12-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 12-5 ISO CLNS Host Cannot Access Hosts in Different Area Level 2 routers are not routing packets to the correct area ES host is not running ES-IS protocol Step 1 Use the trace command to verify that Level 1 routers are routing packets to the nearest Level 2 router. The following display shows...

Iso Clns Host Cannot Access Hosts in Same Area

Symptom Hosts cannot access other hosts in the same area. The hosts might be on the same network or they might be in a different network in the same area. Table 12-4 outlines the problems that might cause this symptom and describes solutions to those problems. Table 12-4 ISO CLNS Host Cannot Access Hosts in Same Area Area address is configured incorrectly on the host Step 1 Check all Level 1 routing tables and link-state databases. Step 2 Verify that the hosts are in the same area. Step 3 Check...

Iso Clns Host Cannot Access Hosts on Local or Remote Network

Symptom Hosts cannot communicate with other hosts. Hosts might be located on the local or a remote network. Connections to some hosts on a network might be possible, whereas connections to other hosts on the same network fail. Table 12-3 outlines the problems that might cause this symptom and describes solutions to those problems. ISO CLNS Host Cannot Access Hosts on Local or Remote Network Missing or mis-configured default gateway specification Level 1 router or ES has bad address Step 1...

Iso Clns Poor Performance

Symptom Users experience poor performance or sudden loss of connections. One or more routers might be receiving duplicate routing updates and might see routers and ESs on multiple interfaces. Table 12-9 outlines the problems that might cause this symptom and describes solutions to those problems. Table 12-9 ISO CLNS Poor Performance Multiple ISO-IGRP processes are configured on a single interface Bridge or repeater in parallel with router Step 1 Use the show clns interface exec command to view...

Iso Clns Redistribution Causes Routing Problems

Symptom Route redistribution does not work properly and causes routing problems. Traffic does not get through a router that is redistributing routes between two different routing areas or domains typically IS-IS and ISO-IGRP. Observed symptoms range from poor performance to no communication at all. Table 12-8 outlines the problems that might cause this symptom and describes solutions to those problems. Table 12-8 ISO CLNS Redistribution Causes Routing Problems Misordered sequence The sequence...

Media Problem Suggested Actions

Use the show interfaces ethernet exec command to determine the status of the router's Ethernet interfaces. The presence of many CRC errors but not many collisions is an indication of excessive noise. Check cables to determine whether any are damaged. Look for badly spaced taps causing reflections. If you are using 100BaseTX, make sure you are using Category 5 cabling and not another type, such as Category 3. Use the show interfaces ethernet command to check the rate of collisions. The total...

Misconfigured Access List Example

Misconfigured access lists can cause connectivity and performance problems. In the environment shown in Figure 7-12, the network administrator can successfully reach Router Z from Router X using the telnet and ping commands. However, when attempts are made to trace the route using the trace command, the connection fails. Figure 7-12 A Misconfigured Access List Sample Network When examining the configuration of Router Y, the network administrator finds the following extended access list...

Modem State Modem Hardware State Meaning

Idle CTS noDSR DTR RTS These are the proper modem states for connections between an access server or router and a modem (when there is no incoming call). Output of any other kind generally indicates a problem. Modem State Modem Hardware State Meaning Ready If the modem state is Ready instead of Idle, there are three Modem control is not configured on the access server or router. Configure the access server or router with the modem inout line configuration command. A session exists on the line....

Multicast Open Shortest Path First

Multicast Open Shortest Path First (MOSPF) is an extension to OSPF, which is a unicast routing protocol that requires each router in a network to be aware of all available links in the network. Each OSPF router calculates routes from itself to all possible destinations. MOSPF works by including multicast information in OSPF link states. MOSPF calculates the routes for each source multicast group pair when the router receives traffic for that pair. These routes are cached until a topology change...

Netbooting Tips

During netbooting sessions, routers behave like hosts. They route via proxy Address Resolution Protocol (ARP), Serial Line Address Resolution Protocol (SLARP) information, Internet Control Message Protocol (ICMP) redirects, or a default gateway. When netbooting, routers ignore dynamic routing information, static IP routes, and bridging information. As a result, intermediate routers are responsible for handling ARP and User Datagram Protocol (UDP) requests correctly. For serial and HSSI media,...

Network Entities

AppleTalk identifies several network entities. The most elemental is a node, which is simply any device connected to an AppleTalk network. The most common nodes are Macintosh computers and laser printers, but many other types of computers are also capable of AppleTalk communication, including IBM PCs, Digital Equipment Corporation VAX computers, and a variety of workstations. The next entity defined by AppleTalk is the network. An AppleTalk network is simply a single logical cable. Although the...

Novell SAPs

The list of Novell SAPs in Table 8-14 is unverified information contributed from various sources. Novell, in an official capacity, does not and has not provided any of this information. Table 8-14 Novell SAPs, Their Descriptions, and Their Decimal and Hex Values Table 8-14 Novell SAPs, Their Descriptions, and Their Decimal and Hex Values NACS Async Gateway or Asynchronous Gateway Bridge Server or Asynchronous Bridge Server Point to Point (Eicon) X.25 Bridge Server Time Synchronization Server or...

Novell Technology Basics

As an NOS environment, NetWare specifies the upper five layers of the OSI reference model. It provides file and printer sharing, support for various applications, such as electronic mail transfer and database access, and other services. Like other NOSs, such as the Network File System (NFS) from Sun Microsystems, Inc., and LAN Manager from Microsoft Corporation, NetWare is based on a client server architecture. In such architectures, clients (sometimes called workstations) request certain...

Password Recovery Procedure Cisco 500CS Communication Server

Lost passwords cannot be recovered from Cisco 500-CS communication servers. The only way to recover from a lost password is to return the communication server to its factory default configuration using the reset button located on the top of the case. The following procedure describes how to restore the Cisco 500-CS to its default configuration. Note When you perform this procedure, your configuration will be lost. Step 1 Power down the communication server. Step 2 Press and hold down the reset...

Password Recovery Procedure IGS Running Software Prior to Software Release

Cisco IGS routers have a bank of DIP switches located on the rear panel. These DIP switches are used to set the hardware configuration register and must be used in the password-recovery process if the router is running system software prior to Software Release 9.1. Note If your password is encrypted, you cannot recover it. You must configure a new password. Figure 24-3 shows the password-recovery procedure for the Cisco IGS running software prior to Software Release 9.1. There is another...

Password Recovery Procedure Platforms Running Earlier Software Releases

Cisco CGS, MGS, AGS, and AGS+ platforms, and Cisco 7000 series routers running software prior to Cisco IOS Release 10.0 from ROM, all have their configuration registers in the hardware, so you must physically change the position of the configuration register jumper during the password-recovery process. It might be necessary to remove the processor card from the router chassis in order to access the hardware configuration register jumper. Consult your hardware documentation for detailed...

Password Recovery Procedure Platforms Running Recent Software Releases

The Cisco CGS, MGS, AGS, and AGS+ platforms, and Cisco 7000 series routers running software prior to Cisco IOS Release 10.0 from ROM, all have their configuration registers in hardware, so you must physically change the position of the configuration register jumper during the password-recovery process. It might be necessary to remove the processor card from the router chassis in order to access the hardware configuration register jumper. Consult your hardware documentation for detailed...

Physical Connections

IEEE 802.3 specifies several different physical layers, whereas Ethernet defines only one. Each IEEE 802.3 physical layer protocol has a name that summarizes its characteristics. The coded components of an IEEE 802.3 physical-layer name are shown in Figure 4-1. Figure 4-1 IEEE 802.3 Physical Layer Name Components Figure 4-1 IEEE 802.3 Physical Layer Name Components A summary of Ethernet Version 2 and IEEE 802.3 characteristics appears in Table 4-1. Table 4-1 Ethernet Version 2 and IEEE 802.3...

Placing Cells on a Physical Transport Medium

After the data is packaged into 53-byte ATM cells, the cells are transferred to the physical layer, where they are placed on a physical transport medium, such as fiber optic cable or coaxial cable. The process of placing cells on the physical medium takes place in two sublayers the physical medium dependent (PMD) sublayer and the transmission convergence (TC) sublayer. Each PMD is specific to a particular physical medium and includes definitions of proper cabling as well as bit timing. The TC...

Possible Causes Suggested Actions

Check to see whether the answering modem has MNP5 error If MNP5 is enabled on the answering modem, disable it. For information on checking or changing the modem configuration, refer to the modem documentation. Use the show appletalk route and show appletalk zones privileged exec commands to determine whether the router can see its ARA routes and zones. Use the show appletalk interface ethernet exec command and make sure that the output matches your Apple network parameters. Change the interface...

Possible Problem

Step 1 Check to see whether the fan is operating. If it is not, check the fan or the 12 V power supply. Step 2 If the system shuts down after being on for a short time, check the power supply. Step 3 If the power supply appears operational, the router might have shut down due to overheating. Ensure that the chassis intake and exhaust vents are clear. Step 4 If the system does not boot up but the System OK LED is on, check the 12 V power supply to make sure it is not faulty. Step 5 If the system...

Possible Problem Area

Step 1 Check to see whether the RP1 LEDs come on when system power is turned on. Step 2 If none of the RP LEDs come on, make sure that both the fan and power supply are functioning properly. Step 3 If the power supply and fans appear operational but none of the RP LEDs are on, an improperly connected RP, SP2 (or SSP3), or interface processor might have hung the bus. Step 4 If the SP (or SSP) Enabled LED is off but any of the RP LEDs are on, make sure the SP (or SSP) is seated in its slot...

Possible Problem Solution

Use the show running-config privileged exec command to view the router configuration. Check for the ip default-gateway global configuration command, ip-address IP address of the router. If the command is missing, add it to the configuration. If the command is present, make sure it specifies the correct IP address. Step 1 Use the show running-config privileged exec command to view the router configuration. Check the boot server address (IP address of a TFTP server or MAC1 address of a MOP2...

Possible Problems

Misconfigured access lists or other filters Step 1 Use the show appletalk globals exec command to determine whether the internetwork is in compatibility mode. Step 2 Enable the appletalk name-lookup-interval global configuration command and use the show appletalk neighbors exec command to determine which specific neighbor (by NBP1 name) is in compatibility mode. Step 3 To resolve the problem, you can perform one of the following actions Upgrade AppleTalk Phase 1 routers to AppleTalk Phase 2 and...

Possible Problems Solution

Active timer value is The active timer determines the maximum period of time that an Enhanced IGRP router misconfigured will wait for replies to its queries. If the active timer value is set too low, there might not be enough time for all the neighboring routers to send their replies to the Active router. Step 1 Check the configuration of each Enhanced IGRP router using the show running-config privileged exec command. Look for the timers active-time router configuration command entry associated...

Preventive Action

When you change a router or interface configuration, enable the debug apple error privileged exec command to log errors Design your network with attention to the direction in which traffic will flow and minimize the number of different zones in the internetwork The debug apple error privileged exec command tracks the progress and status of changes in the internetwork and alerts you to any errors. You can also run this command periodically when you suspect network problems. In a stable network,...

Preventive Action Description

Every router connected to a Every router on an AppleTalk network (that is, on a single cable segment) must agree network must agree on the on the configuration of the network. Therefore, network numbers, cable ranges, timer configuration of that values, zone names, and other parameters should be the same for every router on the Every network number in an Network numbers must be unique throughout the entire AppleTalk network. Duplicate internetwork must network numbers can cause connectivity-...